<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    var str = '123'
    console.log( str )
    console.log( typeof str )

    // console.log( Number(str) )
    // console.log( typeof Number(str) )

    // console.log( str + 123 )  // 123123
    // console.log( str - 123 )  // 0
  </script>
</body>
</html>